USMLE PRACTICE QUESTION #75
TOPIC: Microbiology, pathology, & reproductive.
Today’s question will test your understanding of a commonly tested topic in microbiology (reproductive microbiology/pathology).
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A 26-year-old pregnant woman in her second trimester presents to the clinic with flu-like symptoms, including fever, malaise, and muscle aches. She has no significant past medical history. She reports having a pet cat at home. Vital signs are within normal limits. The causative agent of her symptoms has which of the following characteristics?
A) Macrophages containing amastigotes
B) Motile trophozoites
C) Gram-positive, catalase-positive cocci
D) Trypomastigotes in blood smear
E) Obligate intracellular, spiral-shaped protozoan
F) Intracellular, crescent-shaped protozoan
G) Enveloped, single-stranded RNA virus
Detailed Breakdown of Answers + Correct Answer Below ⏬
ANSWER + QUESTION BREAKDOWN
The MENTAL MODEL used to answer this question comes from our detailed test-taking skills masterclass (check it out if you want to boost your USMLE test-taking skills). Here’s how to think through this question:
Step 1. Read the last line to determine the actual question: “The causative agent of her symptoms has which of the following characteristics?”
Step 2: Is this a first-, second-, or third-order question?
Answer: 2nd order. 1st: Identify which organism is likely to cause her symptoms, and 2nd: Recognize the correct characteristic/feature of the causative organism.
Step 3: Read the vignette carefully and ask yourself: “What are the high-level characteristics of the causative organism?”
Step 4. Look at the answer choices and select the option most closely resembling your final thought from “Step 3” above.
GENERAL ANALYSIS
The clinical presentation of the 26-year-old pregnant woman with flu-like symptoms and a pet cat suggests an infection with Toxoplasma gondii. This organism is known to cause toxoplasmosis, which can be contracted through undercooked meat or contact with cat feces.
ANSWER CHOICES:
CHOICE A: Macrophages containing amastigotes
Explanation: This describes leishmaniasis, which is characterized by skin sores, fever, weight loss, and enlargement of the spleen and liver. The symptoms and exposure don’t match leishmaniasis.
CHOICE B: Motile trophozoites
Explanation: These are associated with either giardiasis or amoebiasis. Symptoms of infection with either would include diarrhea, abdominal cramps, bloating, and nausea. The patient’s symptoms and risk factors don’t match these findings.
CHOICE C: Gram-positive, catalase-positive cocci
Explanation: This is characteristic of staphylococcus infections, which would present with skin findings, pneumonia, and/or endocarditis.
CHOICE D: Trypomastigotes in blood smear
Explanation: This finding would indicate either Chagas disease or African sleeping sickness. The patient is not at risk of either.
CHOICE E: Obligate intracellular, spiral-shaped protozoan
Explanation: A spiral-shaped organism could indicate a borrelia infection, for which the patient is not at risk.
CHOICE F: Intracellular, crescent-shaped protozoan
Explanation: These findings indicate an infection with toxoplasmosis. Flu-like symptoms such as fever, swollen lymph nodes, and muscle aches could all be present. The patient's history of exposure to a cat aligns with toxoplasmosis.
CHOICE G: Enveloped, single-stranded RNA virus
Explanation: These findings could indicate various viral infections, including influenza. The scenario leads us to believe the disease is parasitic rather than viral.
FINAL VERDICT…
Toxoplasma gondii is an intracellular, crescent-shaped protozoa. It causes toxoplasmosis, which can present with flu-like symptoms in healthy individuals. Pregnant women are at risk for more severe complications if infected. Exposure to cat feces and/or undercooked meat is a risk factor.
CORRECT ANSWER: F) Intracellular, crescent-shaped protozoan
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That’s it for question 75!
See ya next time 👋